linux-kernel - Re: [fuse-devel] Horrible mmap write performance (kernel writeback issue?)

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Date:	Sat, 2 Apr 2016 08:34:56 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Jakob Unterwurzacher <jakobunt@...il.com>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [fuse-devel] Horrible mmap write performance (kernel writeback issue?)

On Wed, Mar 30, 2016 at 8:47 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Mon, Mar 28, 2016 at 09:45:53PM +0200, Miklos Szeredi wrote:
>> >> commit 947e9762a8ddefda38aa21e249e6a4fec215cd12
>> >> Author: Tejun Heo <tj@...nel.org>
>> >> Date:   Fri May 22 18:23:32 2015 -0400
>> >>
>> >>     writeback: update wb_over_bg_thresh() to use wb_domain aware operations
>> >
>>
>> Tejun,
>>
>> Any idea why this commit stalls fuse mmap writes?
>>
>> Here's the start of the this thread:
>>
>>   http://marc.info/?l=fuse-devel&m=145008058603261&w=2
>
> Hmmm... cgroup writeback support shouldn't affect fuse at all as the
> backing device doesn't enable cgroup support.  I probably made some
> silly mistake.  Is there a simple reproducer I can play with?
>
> Thanks.
>

To quote Jakob from a previous email:

"I you want to reproduce, clone https://github.com/rfjakob/mmapwrite.git and
run ./encfs-test.sh (needs encfs installed). On the bad kernel, it will hang
within a few seconds."

Hope this helps.

- Sedat -